As most vehicle owners know, engine lubricating oil plays an important role in the proper operation of a vehicle engine. Not only does lubricating oil provide lubrication for the valvetrain and other moving parts in the engine, it also plays an important role in dissipating heat generated by the engine, as well as cleaning moving engine parts. As most vehicle owners are also aware, engine oil requires periodic changing in order to maintain proper engine operation. Heat and impurities in the engine cause the oil, and the additives often contained in the oil, to become dirty and to break down, resulting in reduced lubrication and cleaning ability.
Suggested engine oil change intervals vary depending primarily on the manner in which the vehicle is driven and the conditions under which it is driven. It is known that engine oil temperature contributes significantly to the useful life of the oil. Cold oil temperatures and high oil temperatures both reduce the useful operating life of oil, while a temperature within a certain range provides the longest useful oil life. Thus, as can be seen, harsh operating environments such as extreme cold or extreme heat decrease engine oil life, as does extended operation at high speeds or loads. U.S. Pat. No. 5,060,156 entitled Method and Apparatus for Determining Engine Oil Change Intervals According to Actual Engine Use, to Vajgart et al. describes a system which determines an oil change interval as a function of engine oil temperature.
Known methods of determining oil temperature typically utilize a mechanism, similar to that utilized by Vajgert et al., which employs an oil temperature sensor which transmits a signal indicative of the oil temperature to a control module. The temperature sensor however, imposes an added cost to the engine. Moreover, the temperature sensed by the oil temperature sensor is not always accurate. Accurate determination of engine oil change interval accordingly suffers, engine performance and operational life decrease as a result.
Consequently, there is a need for a system which provides low cost and reliable determinaton of engine oil temperature.